Jeremy Sebens

The UIUC "Chambana Belle" had her maiden flight today, and managed to leave the ground and return to it intact. Modifications are needed, however, as without the expert hands of Mike Cross on the sticks it probably wouldn't have managed the return.

The plane needs a bigger fin, and the extension is going in the bag tomorrow. After wobbling around the sky for a bit, it spun down and was recovered and landed by Mr. Cross (THANK YOU!!!!)

For those that weren't following the side discussion in the SAE Aerodesign thread, the Belle is a moldless composite aircraft. It is powered by a geared Astro 60 turning an 18X18 on 40 CP1300s. It has a wingspan of 8 feet and an overall length just shy of 4.

It is UIUC's entry into this year's AIAA Cessna/ONR Design/Build/Fly Competition: http://www.aae.uiuc.edu/aiaadbf/

Pictures will follow - must cut them down to size.

Jeremy Sebens

On the ground:

Jeremy Sebens

still parked...

Jeremy Sebens

Woohoo!

Jeremy Sebens

ohpleaseohpleaseohplease

Tall Paul

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UGOLEE!!!
Almost short enough to be a flying wing. But WAY too short! You better lock Mike onto that project, there's no one better!

Tall Paul

Fitting mine into the box....
Lots of room!

Tall Paul

And the layout side and front...(Ignore the slimer motor ) I use what I have.

Tall Paul

Actually, I've been looking for a 6 inch wide r/c Humvee... my brother suggested a LAPES inflight release.. which is possible with the open bottom and rear.
Pop the thing out the back during a low pass, and drive it off the pallete.

Jeremy Sebens

But it'd take a while to put that together - remember that's part of our score.

Jeremy Sebens

Yeah, she's a beast, but it only takes about ten seconds to assemble her out of the box. Mike is definitely the best there is, and has generously volunteered his time as pilot for the team in the past. This year, however, I'll be taking over as pilot once the bugs are worked out.

Jeremy Sebens

Oh, and that's not a hatch cover - the black X is actually carbon added into the layup for torsional stiffness.

ilikeplanes

Why is it so short? That's like opening a paint can with a penny. Ya got no leverage.

Tall Paul

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The four foot inside box length determines that, if you don't want a two-piece fuselage.
The teams are scored on assembly time as part of the grade.
Lots of parts takes longer.
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It is a tad or two shorter than I'd care for.
And maybe a bit of dihedral to aid lateral stability, since it spun in. Lots of washour also.. or skip a seperate horizontal completely, make it a wing and pod.
And put a trike gear on it.
That's what neat about these competitions, there's any number of ways to meet the specs.
But the plane MUST fly also.
The easier that is, the more likelihood of a good placement in the results.

Jeremy Sebens

It's definitely short, but has no problem with longitudinal handling.

Let me 'splain what we were thinking:

Lateral stibility isn't what determines "spinability" - rather, it's directonal stability. Anyway, as a high-winger, it actually has a positive dihedral effect, and the directional stability has been addressed with the extended fin.

Trike gear don't have quite as positive a grip on the ground, and ground handling is implortant here. Plus, the taildragger configuration has *much* lower drag.

As to the flying wing, we considered it, but they can't acheive very high Clmaxes. That 120 foot takeoff is a killer!

Mike said that he liked the plane except for the weak yaw stability, so hopefully all will be well. We've more than doubled the tail area, and nearly tripled its AR, so it should be about 3 times more effective now. We fly again at 8:30 tomorrow. I'll let you know how it goes.

Tall Paul

I usually end up cutting vertical area, when the propensity to an uncontrollable spiral dive... not a spin, occurs. There's too small (spin) AND too large (spiral dive) for verticals.
One of the SAE planes in 2000 never made a successful takeoff due to lack of vertical area. It swapped ends every time the wheels left the ground!
I have more trouble with spins with an aft c.g. than anything else.
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That 120 foot distance IS an amusing limit, init?
Need to add lots of lightness.

ilikeplanes

OK, I understand now. I'm a mech engineer so I can appreciate design compromises. In fact, a good way of looking at design challenges is to view them as conflicts. The resolution of design conflicts is what produces a good design.

So, I was reading a book on the history of Boeing. Apparently, they had a lot of trouble in the early days (pre B17) with inadequate yaw stability. The results are very evident with the B17 and B29 designs which had gigantic vertical fins. Anyway, one thing Boeing used on several aircraft was triple vert fins. This would be very easy to implement in your design. They wouldn't need rudders either. Another thing you might try is using a symmetrical airfoil shape. This should help make the fin more effective at a given angle of attack (yaw angle).

Another thought I had was regarding aileron differential. If you have a very heavily loaded wing operating at high Cl, you probably have adverse yaw condition when using ailerons. Aileron differential can counteract this. A good place to start would be 50% more up aileron as down (3:2 up/down ratio). Some model gliders use differential ratios as high as 4:1. The idea is that the drag due to deflecting the ailerons is equal on both sides of the wing. In some cases, like the glider example, a little induced yaw in the turn direction is desirable. Adverse yaw, yaw opposite of the turn, is never desirable.

Good luck.

Tall Paul

For these heavy lifters, I've gone to 100% differential. No down aileron at ALL! Tip stalls are caused by the down-going aileron when the plane is close to max alpha, for the most part.
The flight manuvers aren't that complex, so a limited authority isn't a problem when all you're doing is a few turns. Coupled with rudder, the control is more than adequate.

Jeremy Sebens

After adding to the vertical area, the plane flies BEAUTIFULLY! Mike flew her around the pattern a few times, tested the radome configuration, wrung the plane out with full load, let me try her in the air, and pronounced it good. At that point, I took over as P.I.C. and did some practicing with the plane.

It flies so nicely now - tail follows the nose around, even in 85-degree hard turns. Unloaded, the plane just won't spin - loaded, you have to ask it very nicely to spin, and then if controls are neutralized, it recovers in about 1/4 turn.

The biggest difficulty is the fact that the High-AR wing really floats out on landing - I did break a prop trying to force it down with high alpha flight.

Paul, you're right that a bigger fin will lead to spiral instability, but the time to double on that mode, even with our tremendous vertical, is 92 seconds. That means that if I rolled it to 5 degrees and left it alone, it would be at 10 in a minute and a half - more than half the mission time. That's why, IMO, for these competitions, where the plane only stays steady-state for maybe 10 seconds at a time, the fin should be huge!

ilikeplanes, we are already using a symmetric airfoil (NACA 0009) for both the vertical and the horizontal. No self-respecting aerospace engineer would put plank tails on a plane this big. No reason for it. As to the triple-tail thing, we considered it, but the aspect ratio for each tail remains extremely low, which really kills their sideforce performance. The single tall tail works great, and doesn't really add anything to our assembly time.

Interestingly enough, the plane has "proverse" yaw performance with only about 20% differential. In fact, with elevator input, it hooks hard to the inside, meaning that I have to bank, *then* yank. Roll performance remains excellent even in a stall.

All told, it's a real joy to fly - now if I can just convince it to land where I want it to!

It even drops the payload (anybody figured out where it comes out yet?)

Tall Paul

If you're not equipped with ailerons
the doubling time comes up -REAL- fast!
I've been flying some aileron-less airplanes which are quite picky as to vertical size.
They can achieve some unusual attitudes when you let them go, which can be timeconsuming to escape from!
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You have a slight indication of this with the "proverse" situation.

Jeremy Sebens

Aha! Yes, indeed, rudder-only ships are extremely sensitive to vertical size. I remember the battles I've had with handlaunches in the process of getting the fin/polyhedral all set up just right...

bdb5

My Feedback: (5)

I need to understand, It's truely and unconventional design, but I personally see no advanage to this "concept" of design, what are your goals and were they achieved?? Also, was this a proof of concept design or trial and error? Thanks

Tall Paul

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go here:
http://www.aae.uiuc.edu/aiaadbf/

bdb5

My Feedback: (5)

Still perplex, I'll try and formulate the question.... Ok your all students trying (and achieving) to constuct a RC aircraft. The design is completely original and uses off the shelf components. The design is (according to the link) to achieve flight. To take off, complete a circuit and land. If that is the extent of the requirements, why settle on the design choosen Wouldn't another, less ambious? type be more sutiable for competition? We have all see and are fimiliar with modern aircraft design, I am failing to understand the direction you've chosen?? please help? There are guys in my club who design/build/fly their own aircraft and are out there doing 3D ..... What am I missing??

Tall Paul

Did you read the AIAA rules? Not SAE... a completely different situation.